Increasing evidence demonstrates that an excess of lung cancer and stomach cancer has been observed in workers of iron ore and steel factories. It has been shown that the incidence of cancer is related to the exposure to airborne mineral dusts. However, the active compound(s) responsible for the observed carcinogenicity of mineral dusts has not yet been identified. Although iron oxide (Fe2O3) particles have been tested and found to produce little carcinogenicity, this was likely due to the insolubility of iron oxide in water, even in a slightly low pH medium. Ferrous ion, one of the most abundant elements in polluted industrial environment, is capable of producing reactive oxygen species (ROS), and may play an important role in mineral dust-induced carcinogenesis. Due to the complexity of iron chemistry, previous studies on iron-induced cell transformation did not take into account some important chemical factors. For example, oxidation of Fe(II) to Fe(III) which results in ROS formation is greatly dependent upon the pH of media. Because of the alkaline pH in cell growth medium, oxidation of Fe(II) to Fe(III) takes place quickly in the extracellular medium. Therefore, the short lived ROS resulting from interaction of Fe(II) and O2 may only damage cell membrane which causes cell toxicity. In contrast, when Fe(II) is deposited on a particle, and phagocytized by cells, the released Fe(II) in cells can induce cell transformation. This is relevant to the mineral dust-induced carcinogenesis. The aims of this proposed research are to compare the carcinogenicity of Fe(I) ions in solution and Fe(II)-containing dusts. Different iron compounds will be tested in SHE cell transformation assay. To further determine the mechanism of Fe(II) containing dust-induced carcinogenesis, dichlorofluorescein will be used to estimate oxidant level in cells. 8-oxo-dG and DNA-protein crosslinkings will be measured to detect the DNA damage induced by iron compounds. In addition to SHE cells, we will also investigate the effect of iron compounds on human tracheal epithelial (HTE) cells. Moreover, we will compare the responsiveness of oxidative stress-responsive transcription factors, such as nuclear factor kB and AP-1 to Fe(II) treatment.